The field of art to which the invention relates includes apparatus for the cutting of vegetation, and more particularly to the cutting of vegetation using a flexible, non-metallic cutting line extending from a rotating head into a cutting plane.
Various types of devices have been proposed to facilitate the removal of vegetation by mowing, trimming, edging and like cutting operations. In general, these devices have employed a metal blade to effect vegetation removal. Devices of this nature employ prime movers such as electric and gasoline motors. As a result, rotating metal blades can inflict serious and terrible injury upon the user.
In about 1960, there was developed in Europe a trimmer/edger unit employing a flexible polymeric line extending from a rotating head for cutting vegetation. This unit did not work properly because of several defects in structure and operating parameters. In the United States of America, practical vegetation cutting devices using flexible, non-metallic lines carried upon a rotating head were developed. The devices are shown in U.S. Pat. Nos. 3,708,967, 3,826,068, 3,859,776, 4.035,912, 4,052,789, 4,054,992 and 4,067,108. These patented devices have met with outstanding success in that these American developments provide safe electrical or gasoline-powered tools for vegetation cutting, edging and trimming operations.
The devices shown in the mentioned patents employ a flexible cutting line, such as manufactured from Nylon polymer. The cutting line is carried usually upon a spool internally of a rotating head. When desired to replenish the line or to extend an additional length of line, the rotation of the head was stopped and line manually extended from the spool. This line extension procedure in the patented devices has been found to be convenient, simple and reliable. In many of the more powerful devices, especially those powered by electric motors, a system to extend the cutting line from the head without interrupting cutting operations has long been sought.
A most desirable system would be one capable of feeding cutting line from the head automatically as need was incurred independent of any operator involvement. Structures directed toward this purpose are shown in U.S. Pat. Nos. 3,895,440, 4,020,550 and 4,035,915. These structures have, in common, a basket weave supply of cutting line carried on the periphery of a disc with the line feeding from behind special post members. These post members have a cutting-abrading edge so that cutting line from the weave supply is bent about such edge in the free traveling end portion extending into the cutting plane. The combination function of the edge, line, angular speed, etc. is arranged so that the line posts with such edge sever the free end of the cutting line when it is worn to an ineffective length. In practice, these structures are found to waste about 25 percent of the cutting line because of the excessive length of line severed at the posts' edge, e.g., 3 inches.